This is a continuation-in-part of application Ser. No. 532,910, filed Jun. 4, 1990 now abandoned.
1. Field of the Invention
This invention relates to a diamond dressing unit for dressing grinding wheels and more particularly to a dressing unit having an incremental infeed unit for advancing a diamond roll in relation to a grinding wheel, particularly useful with internal grinders.
2. Description of the Related Art
In the automated production of various parts for machinery for automotive, bearing, aircraft or other industries, precision tolerances and high finishes are required. Such precision grinding has been achieved utilizing diamonds to form and maintain the contours of a grinding wheel which shapes material into the desired part. The importance of precision in grinding cannot be understated since many of the specifications require accuracy to one ten-thousandth or even 2.5 millionths of an inch.
At first, a single point diamond tool was used which was mounted on a cam or a pantograph device and brought into contact with a grinding wheel. The diamond shaped the grinding wheel which in turn shaped the material to the required specifications for forming the machine part.
The single point diamond, although able to shape the grinding wheel to specific precision tolerances, was inefficient because it was time consuming, it increased manufacturing costs and slowed down production and if the diamond chipped, scrap pieces were produced.
A significant improvement in diamond dressing technology came with the development of a diamond formed roll. These diamond rolls were rotatably mounted on a shaft (spindle), and the spindle wa connected to the dressing device. The dressing device advanced the spindle to thereby advance the mounted diamond roll into the grinding wheel for dressing and then retracted the spindle to remove the diamond roll from contact with the grinding wheel after dressing. The diamond roll was brought into contact with the grinding wheel to simultaneously shape the whole grinding wheel. This overcame the disadvantages of the single point diamond by significantly reducing the dressing time.
In one prior art form of the dressing device, the advancing/retracting mechanism was hinged. However, the hinge wore out after frequent use, thus requiring frequent replacement. In another form, the dressing unit was mounted on a slide. However, the slide could not be sufficiently covered to prevent debris from getting inside, therefore causing damage to the parts and adversely affecting the precision dressing.
A beneficial advance came with the development of a sealed cylindrical ram. This apparatus is shown in the brochure No. R5-741 entitled "Clipper Rotodress Diamond Precision Rotodress System", published by Clipper Diamond Tool Co., Inc. This ram was connected to the spindle to advance the spindle and diamond roll into contact with the grinding wheel for dressing and then to retract it after dressing. The ram was heavy, rigid, and provided for maximum vibration dampening. It also required less maintenance compared to the aforementioned hinge and slide mechanisms because the ram, being round, formed a more effective seal which prevented grindings from getting onto the bearing surfaces.
This ram dressing device could be mounted on plain, angle, crankshaft, vertical, centerless or other grinding machines to provide means in situ for correcting grinding wheels by dressing them periodically as they wore down in use. The ram provided for incremental infeed of the diamond roll into the grinding wheel. The incremental infeed ram was controlled with either a stepping motor, a hydraulic indexer, or servomotor.
Although this ram was an improvement over the then existing dressing units, it suffered from deficiencies of its own. It was too large to be used with many internal grinders in which there is a limited amount of space. These internal grinders require the spindle on which the diamond roll is mounted to be able to be rapidly advanced for dressing to differing positions (depending upon the position of the grinding wheel on its cross slide) and to be rapidly retracted to move out of the way of the grinding wheel to permit its usual use. However, retraction of this device could not be accomplished quickly enough with a stepping motor, hydraulic indexer or servomotor and still stay within the space limitations.
The need therefore exists for a dressing unit having a round ram to obtain the advantages of rigidity, minimum vibration and proper sealing, but which could fit within units such as those utilizing internal grinders and allow quick advance to differing positions and quick retraction to a positive stop after dressing.